Rio Grande do Sul (RS) is the southernmost state in Brazil and includes areas within the Pampa and Atlantic Forest biomes. The semiaquatic bugs (Hemiptera, Heteroptera, Gerromorpha) from RS are poorly known, with only 14 previously recorded species. We carried out two expeditions in this state, in 2002 and 2019, across 19 municipalities. Here, we provide new records for 19 species, of which 13 are recorded for the first time from the state, five have their distributions expanded, and one is recorded again from a same locality previously reported in the literature. Furthermore, 13 species were collected for the first time in the Pampa biome and one in the Atlantic Forest.