The development of information and communication technology and smart technology in modern society makes daily life very convenient for modern people, while also causing various side effects. These side effects typically appear in various forms, including cyberbullying, Internet addiction, personal information infringement, and the distribution of harmful information. Especially with the development and distribution of smart devices, smartphone overdependence is very serious, especially among teenagers. The purpose of this study is to analyse the causes of overdependence on smartphones in Korean teenagers and also to suggest solutions. The overdependence of smartphones is represented by three phenomena: self-control failure, salience, and serious consequences. A thorough statistical analysis showed that self-control failure was the largest among the three phenomena of overdependence on smartphones, followed by salience and serious consequences. Teenager smartphone over-dependents personally try to solve smartphone overdependence through strengthening smartphone self-control capability and alternative leisure activities. However, both their main and desired leisure activities are smartphone use, and they want other alternative activities, but they cannot escape using smartphones. It is hoped that the results of this study will help follow-up research in the future along with policy directions on teenagers’ overdependence on smartphones. Keywords—Smartphone Overdependence, Smartphone Addiction; Teenagers, Information and Communication Technology, Smart Technology, Information Ethics