InSb-based materials are promising thermoelectric (TE) alternatives at medium temperature with the high power factor (PF) derived from the intrinsically ultra-high mobility (104–105 cm2 V−1 s−1). N-type InSb-based TE materials have been studied extensively due to the intrinsic Sb vacancies originating from the low formation energy. Based on that π-type TE devices are in favor of P-, N-legs with similar thermal expansivity, P-type InSb-based materials are highly desired. Herein, P-type InSb is synthesized by adjusting the Fermi energy via performing Cd doping. The PF reaches up to ~1.91 × 10−3 W m−1 K−2 at 723 K due to the increased electrical conductivity and inhibited bipolar diffusion effect caused by the high carrier concentration. Furthermore, the lattice thermoelectric conductivity is reduced to 2.0 W m−1 K−1 at 723 K on account of intensive phonon scattering and suppressed bipolar diffusion effect. Finally, benefiting from the simultaneous optimization of the electrical and thermal properties, the optimized figure of merit (zT) value of 0.40 (increased by ~7.0 times) at 723 K was achieved in P-type Cd0.07In0.93Sb, which is comparable with most N-type InSb-based materials. This study could be significant to develop cognate thermostable TE devices using the P-type InSb counterparts.