A new semiconductor waveguide absorption modulator is demonstrated utilizing the heterostructure field‐effect transistor structure. The modulator of 300 &mgr;m length and 10 &mgr;m width achieves an extinction ratio of 8 for a gate voltage change of 2.5 V and an absorption change greater than 2300 cm−1. The transistor transconductance is 92 ms/mm for a 1 &mgr;m device and an identical structure has been reported as an edge‐emitting laser providing an ideal combination for optoeletronic integration.