Option Explicit
Function GetMois(NumSem As Byte) As Variant
Dim cel As Range
Set cel = Range("Tableau1[[Sem1]:[Sem5]]").Find(NumSem, , -4163, 1, 1)
If cel Is Nothing Then GetMois = "?" _
Else GetMois = Worksheets("Matrice").Cells(cel.Row, 11)
End Function