This letter concerns experiments on optically pumped GaN/AlGaN separate-confinement heterostructure laser structures grown by plasma assisted molecular beam epitaxy. The structures were grown along the (1120) nonpolar crystallographic direction on a bulk GaN substrate. Different widths of GaN quantum wells were applied in the studied structures. Laser action is clearly demonstrated by the spontaneous emission saturation, abrupt line narrowing, and strong TE polarization of output light. A lasing threshold was reached at an excitation power density of 260 kW/cm2 for a 700-μm-long cavity at room temperature.