Aluminum alloys have high strength and are easily recyclable owing to their low melting point. Therefore, aluminum is widely used for manufacturing cars and electronic devices. Currently, the most common method for bonding aluminum surfaces is brazing. However, brazing requires positional accuracy and results in the formation of voids by the flux residue; therefore, to avoid these problems, solid-state bonding methods are considered as a possible alternative. However, solid-state bonding also suffers from some problems that need to be overcome. One of these problems is the presence of an oxide film on aluminum surfaces, necessitating the need to remove or destroy the oxide film without applying high temperature and high load. Hence, in this study, a bonding surface was treated with NaOH (aq) for removing the oxide film; moreover, the effectiveness of this treatment was determined by observing the bonding interfaces and fractured surfaces of specimens. For solid-state bonding, the specimens were first subjected to surface modification by boiling the specimens in NaOH (aq) for 20 s. Solid-state bonding was then carried out at bonding temperatures ranging from 693 to 813 K in a vacuum chamber with the bonding pressure and bonding time fixed at 6 MPa and 1.8 ks, respectively. After solid-state bonding, the specimens were subjected to the tensile test for evaluating their strength. The results revealed that the tensile strength of a joint increased with the bonding temperature with or without surface modification. Moreover, surface modification resulted in high-strength joints with less deformation at low bonding temperatures. In addition, the bonding temperature and degree of deformation needed to achieve joints with strength higher than the 0.2% proof stress of aluminum were 100 K and 25% lesser, respectively, in the case of surface modification. On the basis of the experimental results, it was established that surface modification is effective for removing oxide films and processing layers on an aluminum surface.