Several high performance industries (i.e. natural gas compression) require high-speed motors. Solid rotor cage induction motors (SRCIMs) are perfect nominees to such applications, owing to their high reliability. However, the restrictions over ferromagnetic materials and manufacturing process overwhelm the SRCIM design. The motor is required to have low power losses in stator core and the solid rotor. Furthermore, low number of rotor slots is demanded in order to facilitate welding process in rotor side. Those two objectives are contradicting in design stage. This study investigates the losses characteristics of high-speed SRCIM considering the behavior of different ferromagnetic materials, and the complexity of welding process of solid rotors. With a 160-kW and 3000-kW SRCIMs, the influences of stator ferromagnetic material, rotor conductivity, slot combination and air-gap length on power loss characteristics are comprehensively analyzed. Based on the aforementioned analysis, an optimal design criterion for SRCIM is proposed to decline the eddy current losses and decrease the complexity of welding process in the SRCIM's rotor. To verify this criterion, a 160-kW SRCIM prototype is designed and manufactured. Experimental validation is performed and the effectiveness of the proposed design procedure is verified.