This paper presents a new hybrid MAC protocol for wireless sensor network (WSN). The design of our protocol benefits from the low traffic feature of the majority of WSN applications to save energy and increase network lifetime. Our MAC protocol is duty-cycled and hybrid. It is based on multi-band communication and time division in time slots for channel access scheduling. This leads to easier network synchronization technique, which is initiated at base stations and propagated to the networks nodes. Performance analysis, through the presented simulation results, shows important gains in terms of energy saving and latency as compared to the well known S-MAC protocol.