After his senior season at Georgetown, Aw was automatically eligible for the 1998 NBA draft, but he was not selected by an NBA franchise. In December 1998 he signed a professional contract for Belgrano de San Nicolás of the Argentine Liga Nacional de Básquet. In his first season as a professional, Aw averaged 20 points and 5.8 rebounds while shooting 58% from the field over 32 games (35.4 minutes per game). He stayed with Belgrano also for the following season, during which he posted averages of 18.5 points and 6 rebounds per game, with a 65% field goal percentage. In 2000 he played for Gimnasia La Plata in the Torneo Nacional de Ascenso, the second tier of Argentine basketball, and averaged 19.8 points and 6.2 rebounds per game. He then went back to Belgrano for the 2000–01 season, playing 24 games (18.1 points, 5.9 rebounds per game).