There qutie a fiew ways to get the sematic model.

• From a Document class

  Document document = ...;
  SemanticModel semanticModel = await document.GetSemanticModelAsync();
  

• From a Compilationclass

  CSharpCompilation compilation = ...;
  var semanticModel = await compilation.GetSemanticModel(syntaxTree);
  

• From an AnalysisContext. Fro example inside a DiagnosticAnalyzer you can do:

  public override void Initialize(AnalysisContext context)
  {
      context.RegisterSemanticModelAction(x =>
      {
          var semanticModel = x.SemanticModel;
          // Do magical magic here.
      });
  }
  

var syntaxRoot = await document.GetSyntaxRootAsync();

var semanticModel = await document.GetSemanticModelAsync();
var sampleMethodInvocation = syntaxRoot
    .DescendantNodes()
    .OfType<InvocationExpressionSyntax>()
    .First();

var sampleMethodSymbol = semanticModel.GetSymbolInfo(sampleMethodInvocation).Symbol;
var referencesToSampleMethod = await SymbolFinder.FindReferencesAsync(sampleMethodSymbol, document.Project.Solution);