I think it would be helpful for the OP, and other people who are trying to become familiar with Taiwan's personal income tax system, to keep in mind the distinction between "tax withholding rate" and "tax rate." The tax withholding rate determines how much tax the employer withholds from each paycheck in anticipation of tax owed. This withholding rate is determined in advance, and varies depending on factors such as local or foreign nationality and period of residence (there are already lots of threads on this). The tax rate, on the other hand, is the actual rate of tax that applies when the taxpayer files their taxes, and is determined based on how much income the taxpayer has actually earned in the taxable period (which determines what tax bracket the tax payer falls into). A taxpayer who has worked for a year and had tax withheld regularly at a 20 percent withholding rate is likely to get a refund at the end of the year, because their actual tax rate is likely to be lower than the rate at which income has been withheld from their pay (unless the taxpayer falls into a very high income bracket).
A taxpayer may also be able to pay less tax -- i.e. claim a greater refund at the end of the tax period -- by claiming various deductions and exemptions available under Taiwan's tax laws at the time they file their tax.
By the way, I'm not an accountant -- I'm just trying to clarify some very basic concepts that new posters often seem to get muddled.