Purpose: Internships are utilized globally to recruit graduate employees. However, there is a limited understanding of the process by which interns convert into regular employees, particularly in non-Western research contexts. Integrating attraction-selection-attrition (ASA) theory and proactive career behaviors, this study identifies the mechanisms influencing interns' intentions to convert into regular employment in host organizations in Vietnam. Design/methodology/approach: Time lagged, questionnaire data were collected from 669 final-year undergraduate business and economics students who participated in internship programs in a large metropolitan city in Vietnam. Findings: The results indicate that the interns who exhibit proactive career behaviors are more likely to foster high-quality reciprocal relationships with their supervisors and work colleagues during internships. These positive relations magnify interns' intentions to become regular employees via their perceived person-organization fit. Practical implications: This study has implications for higher education institutions and host organizations when designing internship programs to maximize employment outcomes via conversion of interns into regular employees. Originality/value: Previous studies have not tested the critical aspect of ASA theory regarding the personalities of the interns when building work-related relationships that result in the person-organization fit before accepting job offers from host organizations.