A theory is formulated for the static properties of silicon junction field-effect transistors which are compensated with defects with deep energy levels. A single effective level of an acceptortype 0.40 eV below the conduction band accounts satisfactorily for the degradation of heavily doped n-channel devices with neutron irradiation. Furthermore, based on the existence of defect levels, a frequency dependence of the transconductance is predicted and observed experimentally. The charging and discharging of the defects in the junction space-charge region can follow only at low frequencies. At higher frequencies (above 10-100 kHz at room temperature) the trapped charge cannot respond to the signal frequency very rapidly and the transconductance may be several times higher than the low frequency value.