A field-sensitive photoconductive sampling technique has been demonstrated in measurements performed through an insulating layer without the need for conductive contact. Sampled signals are sensed by a virtual-ground, floating-gate amplifier without draining charge from the device under test or the photoconductive switch. The minimum detectable signal is 2.5 μV/Hz1/2 with a spatial resolution of 7 μm, while the sampling bandwidth is essentially that observed using photoconductive sampling with a conductive contact to the device under test. The photovoltaic and shot current noise are negligible in comparison with the lock-in amplifier noise since the current flowing in this high-impedance, floating-gate probe is negligible.