Solenoid-type microtransformers were fabricated by using a photo-definable thick photoresist and through-hole plating techniques to allow three-dimensional multilayer fabrication of the coils. Primary and secondary coils have a low-frequency inductance of 100 and 80 nH, respectively. Flux leakage is a serious problem on devices with coils on opposite sides of the toroid. Interleaved coils, however, have a coupling constant of 0.9 before falling off at frequencies above 500 kHz. The inductance begins to roll off at about 50 kHz because of core effects. The design has an insertion loss of -19.5 dB at 10 MHz.