Domain　ontologies　are　usually　built　by　domain　expert　manually.　They　are　accurate　and　professional　from　the　perspective　of　domain　dependent　concepts,　instances　and　relations　among　them,　nevertheless,　maintaining　and　creating　new　ontologies　need　too　much　manual　work,　especially　when　the　ontology　goes　to　large　scale.　Semi-structured　data　usually　contain　some　semantic　relations　for　concepts　and　instances,　and　there　are　many　domain　ontologies　implicitly　exist　in　these　types　of　data　sources.　In　this　paper,　we　investigate　automatic　hierarchical　domain　ontology　generation　from　semi-structured　data,　more　specifically,　from　HTML　and　XML　documents.　The　main　process　of　our　work　includes　domain　terms　extraction,　pruning,　union　and　hierarchical　structure　representation.　We　illustrate　our　study　based　on　Artificial　Intelligence　related　conference　data　represented　in　HTML　and　XML　documents.　©　2011　Springer-Verlag.