A syntax-directed definition (SDD) is a context-free grammar with attributes attached to grammar symbols and semantic rules attached to the productions. The semantic rules define values for attributes associated with the symbols of the productions. These values can be computed by creating a parse tree for the input and then making a sequence of passes over the parse tree, evaluating some or all of the rules on each pass. SDDs are useful for specifying translations.
So syntax-directed definition is a part of semantic analysis not syntax analysis as it is associated with meaning not only syntax.