We demonstrate a novel architecture for a THz near-field probe, which enables coherent imaging with subwavelength spatial resolution using THz quantum cascade lasers. An InAs nanowire acting as a THz detector based on the field effect transistor concept is integrated inside a subwavelength input aperture of the near-field probe to detect intensity of the THz field and its phase. To determine the phase locally, the THz field is superimposed on the reference THz field incident on the aperture of the probe from the back side. In this configuration, the THz detector exhibits coherent gain and sensitivity to the relative phase between the local and the reference THz fields.