The 21st Russian Young Conference on Physics of Semiconductors and Nanostructures, Opto-and Nanoelectronics was held in Saint Petersburg on November 25 – 29, 2019. It was organized by Peter the Great St. Petersburg Polytechnic University.The program of the Conference included semiconductor technology, heterostructures with quantum wells and quantum dots, opto-and nanoelectronic devices and new materials. A large number of participants with more than 200 attendees from many regions of Russia provided a perfect platform for the valuable discussions between students and experienced scientists.Conference included two invited talks given by the leading scientists, devoted to actual problems and major advances in physics and technology. The keynote speakers were M. A. Semina from Ioffe Institute (presentation “Rydberg excitons in the copper oxide”) and G. S. Sokolovsky also from Ioffe Institute (presentation “Infrared and terahertz quantum cascade lasers”). Students, graduate and postgraduate students presented their results on plenary and poster sessions. The total number of accepted papers published in Russian (the official conference language) was 124. Here we publish 40 of them in English.Like previous years, the participants were involved in the competition for the best report. Certificates and cash prizes were awarded to a number of participants for the presentations selected by the Program Committee. The special E.F. Gross Prize was given for the best presentation in semiconductor optics. Works with potential applications were recommended for participation in the following competition for support from the Russian Foundation for Assistance to Small Innovative Enterprises in Science and Technology.List of The winner of the E.F. Gross Prize for the best presentation in semiconductor optics and Winners of the competition for the best report are available in this PDF.