Transistor testing fixture is intended for connecting of standard coax circuits of measuring devices to the pads of GaAS field-effect transistor chips and for the analysis of low noise and low power transistor microwave parameters in 80…350 K temperature range. It is used local cooling of a tested transistor by vapor-liquid streamflow of liquid nitrogen directed into transistor chip. The changing of tested transistor cooling degree is provided by the variation of liquid nitrogen streamflow.
      Alumina microstrip lines are used in transistor testing fixture. The microstrips lines are ended by signal microprobes (as to say contact needles) made from beryllium bronze. The ground microprobes (for contacting of source transistor pad with ground) are mounted directly on the nose of frame which is separate the input and output of tested transistor. The microprobe inductance is 0.3 nH. The transistor pad dimensions are not less 80x80 mkm.