Crystal homogeneities in liquid‐encapsulated Czochralski grown, semi‐insulating GaAs (100) wafers were evidently improved by annealing at 800 °C for more than 12 h. The improvement was confirmed by observing cathodoluminescence intensity line scanning profile and by measuring field‐effect transistor (FET) threshold voltage standard deviation &sgr;Vth. &sgr;Vthfor 14‐h and 18‐h annealed/polished wafers exhibited about one‐half that for a nonannealed wafer. Direct evidence of the improvement was also obtained by measuring dislocation effect on FET threshold voltage.