A high-brightness diode end-pumped Nd:YAG microchip laser, passively Q-switched by a Cr(4+):YAG saturable absorber (SA), has been developed. The dependences of pulse energy and width were investigated based on theoretical verification to enhance the peak power. As a result, the peak power exceeded 1.2 MW with M(2) = 1.04 and spectrum width Delta lambda < 5.1 pm at a repetition rate of 100 Hz. Brightness of 98 TW/sr x cm(2) was obtained with a supplied average electrical power of 2.3 W. The peak power increased up to 2.1 MW with M(2) = 1.36. Peak power of 1.7 MW was obtained from a 2-cm-diameter x 5-cm-long monolithic laser head.