Clarifying the heat-transfer characteristics with local heating is important for some applications such as microelectronics cooling. This paper presents experimental data on heat transfer and critical heat flux (CHF) for water subcooled (T_sub = 75 K) flow boiling in flat minichannels with height of 0.2−3 mm and width of 10-30 mm under intense local heating (power of up to 1 kW from a heater with an area of 1 cm²) in a wide range of mass flux (10−340 kg/m²s). The growth dynamics of vapor bubbles was studied using high-speed visualization (with the speed of up to 775 000 fps). The obtained data on CHF are compared with the data known from the literature for micro- and minichannels. The results obtained show that the intensity of heat transfer and CHF substantially decrease with decreasing channel height. A decrease in CHF for the channel of 10 mm width (equal to heater width) is revealed, which is caused by more constrained flow conditions in this channel. Several power-law correlations are proposed for estimating CHF in channels with local heating.