The professional competence of teachers has been at the center of interest in recent years, as it is considered an important factor in upgrading education. However, the role of teachers is very complex and constantly changing, as a result there is no precise definition of professional competence. The most studied "quality" characteristics of the teachers are the level of education and the experience gained over the years of service, mainly because they are measurable and used as a measure of

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... chers' salary ranking. Technological competence is added to the characteristics of professional competence since the teachers are called, today, to apply new teaching methods using technology. This created the need for tools, such as Technological Pedagogical Content Knowledge (TPCK) that measures the knowledge of teaching content, pedagogy and technology used by teachers. The purpose of this study is to study the professional competence of teachers in relation to their professional service. It was investigated whether the years of service affect the professional competence of teachers and whether there are differences in professional competence between substitute and permanent teachers of public education in Greece. The quantitative approach was adopted and a TPCK-based questionnaire was created for data collection. The results of the research showed differences in the professional competence of substitute and permanent teachers in Technological Knowledge and Pedagogical Content Knowledge. Substitute teachers seem to have more Technological Knowledge, but less Pedagogical Content Knowledge compared to permanent teachers.