The purpose of the study is to analyze semantic structures in children with speech underdevelopment and describe the algorithm of diagnostic research to arrange a qualitative correctional work to form semantic fields in preschool children with special needs.Research methods include theoretical ones to study psychological and defectological works of scientists and practitioners to analyze the mechanisms of semantic fields formation in children with special needs and practical methods to study the semantic development, and the semantic field of objective activity in mastering the Russian language. These methods provided quantitative data and a qualitative analysis of the responses’ results. 50 children with severe speech disorders attending nursery schools in Bataysk participated in the study.The research results showed that children with severe speech disorders had, in general, a low level of formation in all areas under study: the volume of the passive and active vocabulary, the semantic structure of the word and lexical consistency, word formation, and the semantic field. Conclusions and recommendations. The study provides ample evidence of the need to create a structure of correctional work to form semantic connections in children with various speech disorders. The paper proposes an algorithm for studying the speech functional system of preschoolers.The research findings could be beneficial for speech pathologists and speech therapists, educators and parents to develop preschoolers’ speech, as well as for teachers to elaborate a course of lectures and seminars on teaching methods of correctional work aimed to develop the semantic side of speech in persons with disabilities.