Large area Silicon PhotoMultipliers (SiPMs) are the new frontier of the development of readout systems for scintillating detectors. A SiPM consists of a matrix of parallel-connected silicon micropixels operating in limited Geiger–Muller avalanche mode, and thus working as independent photon counters with a very high gain (~106). This contribution presents the performance in terms of linearity and energy resolution of an electromagnetic homogeneous calorimeter composed of 9~18X0 LYSO crystals. The crystals were readout by 36 4×4mm2 SiPMs (4 for each crystal) produced by FBK-irst. This calorimeter was tested at the Beam Test Facility at the INFN laboratories in Frascati with a single- and multi-particle electron beam in the 100–500MeV energy range.