In this research, watt-class green and blue laser diodes, which are fabricated on free-standing semipolar math formula GaN and conventional c-plane GaN substrates, respectively are developed. Although several research groups have recently developed green laser diodes on semipolar GaN substrates, which have weaker piezoelectric fields and higher indium homogeneity in InGaN active regions compared to c-plane GaN, watt-level output power has yet to be achieved. By utilizing the math formula plane, the first watt-class green lasers at 530 nm is successfully fabricated, and achieve maximum output powers in excess of 2 W, which to the best of our knowledge is the highest value reported for any GaN-based green laser diode. A wall-plug efficiency of 17.5% is realized at a current of 1.2 A under continuous-wave operation, which corresponds to an optical output of approximately 1 W and is the highest value reported to date. In addition, high-power and high-efficiency blue laser diodes at 465 nm are successfully fabricated on conventional c-plane GaN substrates. The output power and wall-plug efficiency are 5.2 W and 37.0%, respectively, at a current of 3.0 A under continuous-wave operation. These laser diodes are promising light sources meeting the ITU-R Recommendation BT.2020 for future laser display applications.