In this letter we report the first observation of enhanced electron mobility in GaN/AlxGa1−xN heterojunctions. These structures were deposited on basal plane sapphire using low‐pressure metalorganic chemical vapor deposition. The electron mobility of a single heterojunction composed of 500 A˚ of Al0.09Ga0.91N deposited onto 0.3 &mgr;m of GaN was around 620 cm2/V s at room temperature as compared to 56 cm2/V s for bulk GaN of the same thickness deposited under identical conditions. The mobility for the single heterojunction increased to a value of 1600 cm2/V s at 77 K whereas the mobility of the 0.3 &mgr;m GaN layer alone peaked at 62 cm2/V s at 180 K and decreased to 19 cm2/V s at 77 K. A 18‐layer multiple heterojunction structure displayed a peak mobility of 1980 cm2/V s at 77 K.