A smartphone addiction scale (SAS) was developed and validated to assess smartphone addiction based on the Korean self-diagnostic program for Internet addiction (K-scale) and smartphone features. The study involved 197 participants aged 18–53 years, with 64 males and 133 females. Factor analysis and other statistical methods were used to evaluate the reliability and validity of the SAS. The scale was revised to include six factors: daily-life disturbance, positive anticipation, withdrawal, cyberspace-oriented relationship, overuse, and tolerance. The internal consistency of the SAS was high (Cronbach’s alpha = 0.967), and it showed significant correlations with the K-scale and Y-scale, which are used to assess Internet addiction. The SAS also demonstrated strong concurrent validity with the Visual Analogue Scale (VAS) scores for each factor. The study found that participants with higher education levels and professionals had lower SAS scores, while students and those with lower education levels had higher scores. The SAS was found to be a reliable and valid tool for assessing smartphone addiction. The study also highlighted the need for further research on the relationship between smartphone addiction and other psychological factors, as well as the development of a shorter version of the SAS for improved convenience. The SAS consists of 48 items grouped into six subscales, each scored on a 6-point scale. The total score ranges from 48 to 288, with higher scores indicating more severe smartphone addiction. The study provides the first diagnostic scale for smartphone addiction and contributes to the understanding of smartphone-related addictive behaviors.A smartphone addiction scale (SAS) was developed and validated to assess smartphone addiction based on the Korean self-diagnostic program for Internet addiction (K-scale) and smartphone features. The study involved 197 participants aged 18–53 years, with 64 males and 133 females. Factor analysis and other statistical methods were used to evaluate the reliability and validity of the SAS. The scale was revised to include six factors: daily-life disturbance, positive anticipation, withdrawal, cyberspace-oriented relationship, overuse, and tolerance. The internal consistency of the SAS was high (Cronbach’s alpha = 0.967), and it showed significant correlations with the K-scale and Y-scale, which are used to assess Internet addiction. The SAS also demonstrated strong concurrent validity with the Visual Analogue Scale (VAS) scores for each factor. The study found that participants with higher education levels and professionals had lower SAS scores, while students and those with lower education levels had higher scores. The SAS was found to be a reliable and valid tool for assessing smartphone addiction. The study also highlighted the need for further research on the relationship between smartphone addiction and other psychological factors, as well as the development of a shorter version of the SAS for improved convenience. The SAS consists of 48 items grouped into six subscales, each scored on a 6-point scale. The total score ranges from 48 to 288, with higher scores indicating more severe smartphone addiction. The study provides the first diagnostic scale for smartphone addiction and contributes to the understanding of smartphone-related addictive behaviors.