The stimulated emissions from semipolar InGaN laser diode (LD) structures grown on (1122) GaN substrates are observed at room temperature under photopumped conditions. The measured emission peaks are in the photon energy range from 2.62 eV (474 nm) to 3.05 eV (405 nm), and the emission intensity has a threshold behavior with respect to the pumping power. A strong in-plane optical anisotropy is observed between the two perpendicular directions, [1 123] and , due to anisotropic matrix elements, which depend on the crystal orientation; the stimulated emission measured along the [1 123] direction occurs with a lower threshold pumping power at a lower energy compared to that obtained along the  direction. The experimental results and the valence band calculations indicate that the transverse-electric mode with an electric vector along the  direction is dominant for gain formation in semipolar and nonpolar InGaN LDs. Compared to c-plane InGaN LDs, semipolar InGaN LDs have comparable or less threshold pumping powers.