The increase in junction temperature is an important factor affecting the output power of master oscillator power amplifier (MOPA) diode laser chip. To achieve the packaging and efficient heat dissipation of the multi-electrode MOPA semiconductor laser chip, a packaging structure that combining P-side up with heat spreader was proposed. An analytical three-dimensional thermal model was employed to study the influence on junction temperature between the P-side down, P-side up without heat spreader and P-side up with heat spreader. According to the three-dimensional thermal model, the conduction-cooled capability between P-side up with heat spreader and P-side down is uniform in this paper. Moreover, the packaging can lead to a maximal 40% decrease on junction temperature. By the way, the P-side up with heat spreader structure was used in MOPA diode laser chip in experiment then 10.5 W output power and the spectrum width (FWHM)＜0.1 nm of the MOPA chip were obtained in CW mode.