A W-band CMOS dual-balun-based four-way power divider is reported. The power divider can be applied to a four-way power amplifier (PA) for four-way power dividing or a star mixer for converting the single RF (or LO) input signal to dual differential RF (or LO) signals. The power divider occupies a small chip area of 0.065 mm² and achieves S11 smaller than --10 dB for frequencies of 87.3~101.1 GHz. For frequencies of 90°100 GHz, the power divider achieves S₁₁ of -10.5~ -12.3 dB, S₂₁ and S₄₁ of -8.09-8.31 dB, S₃₁ and S₅₁ of -7.9~-8.45 dB, and amplitude imbalance magnitude (AIM) of 0-4.19 dB and phase difference (PD) of 176.8°-178.1° for ports 2-3 and 4-5. Moreover, the proposed four-way PA achieves output power (P_out) of 15.2 dB m and power-added-efficiency (PAE) of 16.8 dB m at 94 GHz, better than those (P_out of 12.1 dB m and PAE of 7.7% at 94 GHz) of the traditional four-way PA that uses three Wilkinson power dividers for four-way power dividing. The prominent results of the PA indicate that the power divider is suitable for W-band PAs and star mixers.