Quantitative measurements of an electrical field and impurity profiles in metal-semiconductor field-effect transistor (MESFET) are obtained by using the scanning electron microscopy-dark voltage contrast (SEM-DVC) technique. The measurements require the taking of an image of a MESFET with all electrodes grounded and an image of the same transistor under de bias, the subtraction of one image from the other, and the calibration of the contrast in accordance with the voltages at the drain and gate electrodes. Digital image processing allows us to measure the field profile along the channel of a transistor and to reconstruct the doping profile. Two types of GaAs MESFET with recessed gates were measured : one with a 1-mu m-long gate and another with a 0.5-mu m-long gate. In the field-effect transistor (FET) with the longer gate, we observed that failure to pinch-off is related to doping irregularities in the channel. The submicron MESFET was used to study the dynamic behavior of the field-effect transistor. While changing the gate voltage, the response of the MESFET was videotaped, in an effort to observe the appearance of hot electron areas in the channel. The new quantitative SEM-DVC technique was established in studies of Zener diodes, photodetectors, solar cells, and FETs. The dynamic behavior of these devices was also videotaped.