This paper addresses the problem of channel estimation using pilots in hybrid analog/digital massive multiple-input multiple-output (MIMO) systems for future millimetre wave (mmWave) communications. To further reduce system cost and implementation complexity, we consider an alternative architecture derived from RF switches as opposed to the phase shifters in the conventional literature. The channel estimation is formulated as a combinatorial optimization problem where the aim is to minimize the mean square error (MSE) between the real and estimated channels over a finite set of allowed values for the precoder switches. A genetic algorithm (GA) is developed for solving this problem and obtaining the MIMO channel estimates. Simulations show that the proposed scheme can estimate channels as accurately, if not more, as an existing solution using phase shifters.