Mahayana Buddhism《Hīnayāna and Theravāda (from wiki)》

19th century Western writers seem to have generally regarded Hinayana or 'small vehicle' as a synonym for Theravada or regarded the Theravada school as being one of the Hinayana schools described in Mahayana literature. As later scholarship has clarified the historical relationship between the various schools of Mahayana and non-Mahayana Buddhism this usage has declined among scholars. Theravada Buddhists writing for Western audiences have sometimes attempted to clarify this distinction. As Walpola Rahula noted in his Gems of Buddhist Wisdom:

“We must not confuse Hīnayāna with Theravāda because the terms are not synonymous. Theravāda Buddhism went to Sri Lanka during the 3rd Century B.C. when there was no Mahāyāna at all. Hīnayāna sects developed in India and had an existence independent from the form of Buddhism existing in Sri Lanka. Today there is no Hīnayāna sect in existence anywhere in the world. Therefore in 1950 the World Fellowship of Buddhists inaugurated in Colombo unanimously decided that the term Hīnayana should be dropped when referring to Buddhism existing today in Sri Lanka Thailand Burma Cambodia Laos etc. This is the brief history of Theravāda Mahayāna and Hīnayāna.”

Theravada should not be considered a "Hinayana" school from the Mahayana perspective for unlike the Sarvastivada school which was the primary object of Mahayana criticism the Theravada does not claim the existence of independent dharmas; in this it maintains the attitude of early Buddhism. On the contrary some contemporary Theravadin figures have indicated a sympathetic stance toward the Mahayana philosophy found in the Heart Sutra and the Fundamental Stanzas on the Middle Way. The Mahayanists were bothered by the substantialist thought of the Sarvastivadins and Sautrantikas and in emphasizing the doctrine of emptiness Kalupahana holds that they endeavored to preserve the early teaching.The Theravadins too refuted the Sarvastivadins and Sautrantikas (and other schools) on the grounds that their theories were in conflict with the non-substantialism of the canon. The Theravada arguments are preserved in the Kathavatthu.