In this contribution, three new species of sternaspids collected from sediments along the coast of southern Thailand are described: Petersenaspis apinyae sp. nov. from a depth of 50–80 m offshore in the Gulf of Thailand; P. narisarae sp. nov. from 9 m depth in the Songkhla Sea, Gulf of Thailand; and P. pakbaraensis sp. nov. from tidal mudflats on the Andaman Coast. All three species resemble P. palpallatoci Sendall & Salazar-Vallejo, 2013. They differ mainly in the pigmentation and shape of the shield, the number of ventral chaetae and chaetae at the posterior shield, body papillae, and size of the abdomen. Further, P. apinyae sp. nov. is clearly distinguished from other species of the genus by having dark orange to red butterfly wing-shaped shields, with strongly curved anterior margins. P. narisarae sp. nov. differs from other species by having concentric colored bands over shields and an expanded oval abdomen. P. pakbaraensis sp. nov. can be distinguished from other species by its dark brown-purple shield and laterally expanded fan. These three species have a unique character in their branchial plates: long brownish filaments. A key to the identification of all species of Petersenaspis is included.