A microwave detector based on the thermoelectric effect of warm carriers in bulk semiconductors is described. An analysis of device performance is presented, which is based on the assumption of a Maxwell-Boltzmann distribution for the heated carriers. The performance of a number of experimental devices at millimeter and centimeter wavelengths is shown to be in good agreement with analytic predictions. Outstanding characteristics of these devices are high detection sensitivity, high burn-out power, and high electrical stability over long periods of use.