The flow boiling characteristics of deionized water in horizontal minigap channels filled with metal foams at high heat fluxes were experimentally investigated. The metal foams are made of copper with the PPI of 20 or 40 and the porosity of 0.95. The working conditions include the mass flux of 200-400 kg m^-2 s^-1, the gap height of 0.5-2 mm and the heat flux up to 400 W cm^-2. The result show that he the heat transfer coefficients of the 40 PPI metal foam filled channel are 143% higher than those of the 20 PPI one on average at the same working conditions. The results show that the heat transfer coefficient shows three trends with mass flux: The heat transfer coefficient firstly increases then decreases, and finally is almost unchanged with increasing mass flux, where single-phase convection, subcooled flow boiling, and saturated flow boiling dominate the heat transfer, respectively. At thehigh heat fluxes, the local heat transfer coefficient increases with the increasing channel height. Compared with the plain channel with the same dimensions, the 40 PPI metal foam delays the nucleate state boiling, and increases the heat transfer coefficient by 133% and the critical heat flux by 109% on average. The metal foam has a strong effect of heat transfer enhancement at the low heat fluxes, and has a weak effect at the high heat fluxes, and weakens the heat transfer enhancement with increasing mass flux at the high heat fluxes.