The current voltage relationships of AlGaAs/GaAs modulation doped field effect transistors (MODFETs) were measured as a function of applied uniaxial stress. Stresses in the  and  directions on MODFETs that were grown on a (001) substrate produced threshold shifts of opposite sign. Stresses in  and  directions resulted in threshold voltage pressure coefficients of -15 and 64 mV/Kbar, respectively. The asymmetric shifts in the threshold voltages are attributed to piezoelectric effects. In addition, stress induced changes in the slopes of the transconductance versus gate-to-source voltage relationships were also measured. For stresses in the  and  directions, the dependencies were 0.4 and -0.7 mS/(V Kbar), respectively.