Semi-sweet chocolate is originally an American term, popularized by Nestle Toll House semi-sweet chocolate chips.  Semi-sweet chocolate has at least 35% cocoa solids, but sweeter than bittersweet.  However, the lack of regulations concerning sugar content means that these classifications are relative and not consistant across brands. Semi-sweet chocolate generally has half as much sugar as cocoa and is a sweeter type of dark chocolate. Semi-sweet chocolate is more commonly used for cooking purposes.