The Business Process Modelling Notation 2.0 (BPMN 2.0) choreography is a de factor standard for capturing the interactions between business processes. Flow-oriented BPMN 2.0 choreographies can exhibit a range of semantic errors in the control flow. The ability to check the semantic correctness of choreographies is thus a desirable feature for modelling tools based on BPMN 2.0 choreographies. However, the semantic analysis of BPMN 2.0 choreographies is hindered by the lack of formal semantic definition of its constructs and the corresponding analysis techniques in the BPMN 2.0 standard specification. This paper defines a formal semantics of BPMN 2.0 choreographies in terms of a mapping to WF-nets. This defined semantics can be used to analyze the structural errors and the control flow errors of BPMN 2.0 choreographies with analysis techniques of Petri nets. The proposed mapping and the semantic analysis have been implemented as a tool. The experimental results show this formalization can identify the semantic errors of choreographies from the BPM AI process model library.