This study aimed to develop a self-diagnostic scale for smartphone addiction, the Smartphone Addiction Scale (SAS), based on the Korean Self-Diagnostic Program for Internet Addiction (K-scale) and smartphone features. The reliability and validity of the SAS were evaluated using factor analysis, internal consistency tests, t-tests, ANOVA, and correlation analysis. A total of 197 participants were included, with a mean age of 26.06 years (SD = 5.96). Factor analysis identified six factors: daily-life disturbance, positive anticipation, withdrawal, cyberspace-oriented relationship, overuse, and tolerance. The SAS demonstrated high internal consistency (Cronbach's alpha = 0.967) and concurrent validity, showing significant correlations with the K-scale and the modified Kimberly Young Internet Addiction Test (Y-scale). The VAS scores for each factor also showed significant correlations with the SAS subscales. Differences in job, education level, and self-reported smartphone addiction scores were found among participants. The study concluded that the SAS is a reliable and valid tool for assessing smartphone addiction, providing a diagnostic framework for clinical use.This study aimed to develop a self-diagnostic scale for smartphone addiction, the Smartphone Addiction Scale (SAS), based on the Korean Self-Diagnostic Program for Internet Addiction (K-scale) and smartphone features. The reliability and validity of the SAS were evaluated using factor analysis, internal consistency tests, t-tests, ANOVA, and correlation analysis. A total of 197 participants were included, with a mean age of 26.06 years (SD = 5.96). Factor analysis identified six factors: daily-life disturbance, positive anticipation, withdrawal, cyberspace-oriented relationship, overuse, and tolerance. The SAS demonstrated high internal consistency (Cronbach's alpha = 0.967) and concurrent validity, showing significant correlations with the K-scale and the modified Kimberly Young Internet Addiction Test (Y-scale). The VAS scores for each factor also showed significant correlations with the SAS subscales. Differences in job, education level, and self-reported smartphone addiction scores were found among participants. The study concluded that the SAS is a reliable and valid tool for assessing smartphone addiction, providing a diagnostic framework for clinical use.