Tomashyk is a specialist at the high international level in the field of solid-state and semiconductor chemistry, including physical-chemical analysis and the technology of semiconductor materials. He was head of research topics within the International program “Copernicus”. He is a member of Materials Science International Team (Stuttgart, Germany, since 1999) which prepares a series of prestigious reference-books under the title Ternary alloys and Binary alloys, and has published 35 chapters in the Landolt–Börnstein New Series. Tomashyk is actively working with young researchers and graduate students, and under his supervision, 20 PhD theses were prepared. For many years, he is also a professor at Ivan Franko Zhytomyr State University in Ukraine.