Since 8 February 2018, foreigners who would like to work more freely and more conveniently in Taiwan may apply for Taiwanese Gold Card, which combines work permit, resident visa, alien resident certificate, and re-entry permit. During the valid period of the Taiwanese Gold Card, card holders may freely seek jobs and change jobs in Taiwan. Moreover, the Taiwanese Act for the Recruitment and Employment of Foreign Professionals ("Act") was also amended to provide tax incentives for foreigners who are qualified for Taiwanese Gold Card. However, the requirements for such tax incentives are tricky and somewhat not easy to satisfy.
From 2018, if a foreigner engages in professional work and meets certain requirements, qualified to obtain Taiwanese Gold Card means that he may enjoy tax incentives up to 5 years. The period of 5 years starts from the tax year when the card holder for the first time meets the conditions of residing in Taiwan for 183 days or more, and having a salary income of more than NTD 3,000,000 (approximately, USD 100,000). The tax incentive is that only the NTD 3,000,000 salary income and half of the amount above the NTD 3,000,000 in each tax year shall be included in the gross income for the assessment of individual income tax liability. In short, for the income more than NTD 3,000,000, it looks like that there will be 50% off in terms of taxes. Moreover, foreigners who obtain employment (work) permits issued by the Ministry of Labor or by the Ministry of Education as foreign specialist professionals may also enjoy such tax incentives. However, in either scenario, more additional requirements which are not easy to ascertain need to be met. 

The first requirement: approved to reside in Taiwan for the first time because of work
Article 3 of Regulations Governing Reduction and Exemption of Income Tax of Foreign Specialist Professionals ("Regulations") other than the Act provide for the additional requirements to enjoy tax incentives. First, the foreigners must be approved to reside in Taiwan "for the first time because of work". This is a very tricky requirement. 
When a foreigner has been working in Taiwan with work and resident permit of "general" foreign specialist (that is, not a foreign specialist professional), this will be considered as the first time working in Taiwan. Of course, such a foreigner will not be able to enjoy any tax incentive under the Act because he is not a foreign specialist professional and because he is not holding a Taiwanese Gold Card. This makes sense. But what will happen next? When such a foreigner turns to obtain a Gold Card, or, an employment (work) permit issued by the Ministry of Labor or by the Ministry of Education as a foreign specialist professional, with tax incentive expectations, he will still not be able to enjoy them according to the Regulations. The reason being that now residing in Taiwan will be considered as the second time approved to reside in Taiwan for work. This is the first requirement and also the first trap for those foreigners who have already worked in Taiwan but would like to change their work status, such as applying for a Taiwanese Gold Card. 
To satisfy the first requirement, foreigners will have to prove that their previous staying in Taiwan are for the purpose of "dependents" or "study". For those foreigners who have been previously approved to reside in Taiwan but not based on the reason of engaging in the professional work, fortunately, the first requirement will be exempted. 

The second requirement: engaging in professional work related to recognized specific expertise in Taiwan
The second requirement for the tax incentives is that the foreigners must engage in professional work related to recognized specific expertise in Taiwan. The tax office will check your employment contracts and other documents to examine whether you are working in the recognized specific expertise. That being said, if the recognized specific expertise of yours is science but you are working as a lawyer for a reputable law firm, you will get into trouble. Even though you are admitted to bar in Taiwan or other jurisdictions, in this hypo you are not engaging in professional work related to your recognized specific expertise, science. Foreigners may feel free to change your jobs, but please stay in your recognized specific expertise to avoid a second trap when the tax incentive is your primary goal.
The third requirement: no household registration in Taiwan and not considered as a Taiwanese tax resident for the prior 5 years
The first prong of the third requirement looks very easy to understand. When Taiwan has very strict household registration policy, few foreigners would be able to be registered in front of the Household Registration Office. Put it simply, for example, foreigners need to be naturalized as a Taiwanese citizen and reside in Taiwan for a certain period of time for the registration. 
However, the second prong could be somewhat confusing. Let's start from here: what could make you a Taiwanese tax resident? As the tax office has the discretion to balance many factors to decide whether you are a Taiwanese tax resident, the simplest way is to check whether you have stayed in Taiwan for more than 183 days in a given year. Thus, if a foreigner stays in Taiwan for any reason more than 183 days in a given year, within 5 years prior to his Gold Card is approved, no tax incentives will be granted. For example, when a foreigner gets his Gold Card approved in January 2023 but happen to live in Taiwan for 184 days in February 2018, that will make the tax incentive gone.

When both the Act and the Regulations do not state clearly about the definition of Taiwanese tax resident, and when they even use more vague terms referring to the Income Tax Law, the third requirement is a more invisible trap in terms of applying for tax incentives. Moreover, if you do apply for the tax incentive and fail to satisfy the requirements or other laws, the tax office will order you to pay the taxes you are supposed to pay, OR, on top of that, give you additional fine. A trap? No, more like mines, everywhere. Foreigners truly need to engage a Taiwanese lawyer before applying for employment permit, Taiwanese Gold Card, or tax incentives.