Background: In the last few decades, researchers have turned their attention to students' understanding of scientific concepts at different school levels. The results indicate that the learners have different ideas, and most of them are inaccurate in terms of those generally accepted by the scientific community. Purpose: This study was undertaken to describe the development, validation and use of a three-tier multiple-choice diagnostic test (PEMT) to reveal Turkish high school students' common misconceptions in terms of the photoelectric effect. Sample: In this study, 243 students (male = 86, female = 137) from six high schools made up the sample which comprised approximately 76% of the 11th grade population. Design and Methods: Based on findings from the literature, open-ended questions and interviews, the PEMT was developed and administered to 243 students. The data was analysed descriptively. Results: The Cronbach's alpha reliability coefficient of the scores was estimated as 0.83. Construct, content and face validities were established by senior experts and through the use of statistical techniques. The findings denoted that the test is a valid and reliable measure of students' qualitative understanding of the photoelectric concept. The results revealed that the majority of the students demonstrated a limited understanding of the photoelectric effect and have five prevalent misconceptions. These are: (1) an increase in intensity would provide the photon with enough energy to release electrons; (2) the photoelectric effect results from the ionization of atoms through the interaction with light; (3) a light beam whose photons have smaller energies than the work function would release electrons with the help of a voltage source; (4) the number of photoelectrons depends on the energy of the photon and (5) the photon has kinetic energy and it depends on the colour of light. The last two misconceptions were discovered in the current study. Conclusion: The findings indicated that the PEMT is a reliable and valid measuring tool for investigating high school students' conceptual understanding and misconceptions. Future studies could use the PEMT as a tool for assessing the misconceptions of high school students, pre-service science or pre-service physics teachers.