High-power vertical-cavity surface-emitting lasers (VCSELs) are processed using a wet thermal-selective oxidation technique. The VCSEL chips are packaged by employing three different bonding methods of silver solder, In-Sn solder, and metalized diamond heat spreader. After packaging, optical output power, wavelength shift, and thermal resistance of the devices are measured and compared in an experiment. The device packaged with a metalized diamond heat spreader shows the best operation characteristics among the three methods. The 200 \mu m-diameter device bonded with a metalized diamond heat spreader produces a continuous wave optical output power of 0.51 W and a corresponding power density of 1.6 kW/cm² at room temperature. The thermal resistance is as low as 10 K/W. The accelerated aging test is also carried out at high temperature under constant current mode. The device operates for more than 1000 h at 70 ℃, and the total degradation is only about 10%.