This report describes the implementation of an original liquid-phase epitaxy (LPE) technique using a Ga–Al solution. An N-polar AlN thin film prepared using a sapphire nitridation method was employed as the template for the LPE growth process. The growth behavior depended on attaining a competitive balance of the polarity inversion and the dissolution reaction of the AlN thin film. Therefore, to improve the overall LPE process, it was crucial to understand exactly when and how the AlN thin film dissolved in the solution. This study investigated the dissolution of the N-polar AlN thin film into liquid Al and the resulting AlN growth through in situ observation experiments. The AlN thin film dissolved at a lower temperature than the required temperature for AlN growth. On the basis of these findings, we designed an LPE growth process to obtain a homogeneous AlN layer without the dissolution of the N-polar AlN thin film. Ultimately, a homogeneous AlN layer was successfully formed on the nitrided sapphire substrate using Ga-60mol%Al at 1300 °C for 5 h.