We investigated the malfunction and destruction characteristics of microcontroller devices under narrow-band high power electromagnetic (NB-HPEM) wave by magnetron. NB-HPEM wave was rated at a microwave output of 0 to 1000 W at a frequency of 2460 +/- 50 MHz, and was radiated from an open-ended standard rectangular waveguide (WR-340) to free space. The influence of different reset, clock, data, and power supply line lengths was tested. The variation of the lines length was done with flat cables. The susceptibility of the tested microcontroller devices was in general strongly influenced by clock, reset, and power supply line length, and was only slightly influenced by data line length. Furthermore, as the line length was increased, the malfunction threshold decreased as expected, because more energy was coupled to the devices. The surfaces of the destroyed microcontroller devices were removed and the chip conditions were investigated with a microscope. The microscopic analysis of the damaged devices showed component and bondwire destruction such as break-throughs and melting due to thermal effects. Our results are expected to provide fundamental data for interpreting them combined mechanism of microcontroller devices in an intentional microwave environment.