I am a foreigner, do I need to pay tax to the US government ?

Generally, you will earn profit from capital gain and dividends when you do the stock investment. As an incentive to invest in the US stock market, a foreign investor doesn’t need to pay the tax for capital gain to US government. However, a 30% tax for the dividends is required no matter which country resident you are. For instance, you are given $1 dividend, you will get $0.7 after tax.