In this paper, the concept of multi-phase hybrid buck and boost converters (MP-HBUC and MP-HBOC), is presented. By using single-phase hybrid buck and boost converters (HBUC and HBOC), the proposed MP-HBUC and MP-HBOC significantly reduce conduction loss as compared to the conventional buck and boost converter (CBUC and CBOC). Thus, the proposed MP-HBUC and MP-HBOC maintain high efficiency at heavy loads. Furthermore, the proposed MP-HBOC achieves a minimum-phase characteristic (without right half-plan zero); therefore, the bandwidth and load transient response of the proposed MP-HBOC can be respectively much wider and faster than a CBOC. Implemented in PSIM with extensive analysis, a two-phase hybrid boost converter showed a max/min efficiency up to 97.16 % and 91.3 %, respectively, over a load current of 0.25 10 A at 12 V input, 18 V output voltage. The efficiency improvement is up to 4.95 % at the maximum load. This work can be considered as the very first reported combination of multi-phase and hybrid concepts to design high power-efficient buck/ boost converters for automotive applications.