The single-event response of 3-D Multi-Channel nanowire MOSFETs (MCFET) is investigated using 3-D numerical simulation. The variation with time of the main internal parameters (electrostatic potential and electron density) of the MCFET after the ion strike is analyzed in detail. The drain current transients and collected charge depend on the ion strike location, direction, and track radius. The lateral spacing between adjacent nanowire stacks is found to be a key-parameter in the analysis of the worst case location of the ion strike.