Semelai is an Austroasiatic language spoken in the Malay Peninsula by Semelai people. It belongs to the Southern branch of the Aslian language subgrouping. The Semelai people reside predominantly around the Bera, Serting and associated river systems in the states of Pahang, Negeri Sembilan and Johor.

Semelai is a split ergative language motivated by semantics and word order shift.

Semelai has 32 consonants and 20 vowels.

Vowels are also distinguished with nasal counterparts:

Semelai has many inchoative verbs such as rmɔl "to be male", hitam "be black", which at the first glance may hint a flexible language like nearby Austronesian languages. However, the vast majority of Semelai lemmas can be identified unproblematically to a particular word category. Verbs and nouns must undergo derivation via infixation or prefixation in order to function as other lexical categories, eg. rlmɔl "male" → rmɔl "to be male", yɔk "take" → nk-yɔk "taking INF". Loan words from Malay and Austronesian are mostly precategorial, eg. tuŋkɒt "a stick, to prop up". The language recognizes several distinct parts of speech that are morphologically and syntactically distinguished: the superclass nominal (which includes nouns as an open word class); verb; expressive; preposition; adverb; auxiliary; existential and ascriptive predicators; negator; connective; interjection.

These pronominal clitics are used to mark agreement with the ergative argument of transitive verbs and highly volitional argument of intransitive, human activity-denoting verbs.