The purpose of the study was to explore the association among suicidal ideation, cyber addiction, and school bullying of Korean high school students. This descriptive cross-sectional study included 416 students. The data were collected using structured questionnaires on suicidal ideation, Internet and smartphone addiction, experiences of school bullying, impulsiveness, and depression. Students who were bullied (odds ratio [OR] = 3.0, 95% CI [1.1, 8.4]) and more depressed (OR = 10.8, 95% CI [2.4, 48.2]) were more likely to have higher scores for suicidal ideation; however, when a lower stringency was used, female gender (OR = 2.3, 95% CI [1.3, 4.0]) and addiction to smartphones (OR = 2.4, 95% CI [1.1, 5.4]) were also statistically significant contributors to the presence of suicidal ideation. Students with suicidal ideation that is higher than average, but lower than the classical thresholds for risk group designation, should also be carefully assessed for early detection and intervention. Cyber addiction may be a particularly significant contributor to suicidal ideation, in addition to bullying and depressive mood, among Korean adolescents.