Using a "Do Until" loop to convert decimal numbers to hexadecimal

I am working on program that requires I use a Do-Until Loop to convert a decimal number to hexadecimal number. The following UDF makes Excel freeze up every time I run it, but it works great when I take out the do-until loop. Is there a better way to use a Do-Until Loop in this function?

Function DecHexConverter(DecValue As String) As String
Dim sTemp As String

Do Until DecValue = ""
    If DecValue >= 16 Then
            'if greater than 16 then recall function
            sTemp = DecHexConverter(DecValue \ 16) & DecHexConverter(DecValue Mod 16)
    
    ElseIf DecValue > 9 And DecValue < 16 Then
            'if between 10 and 15 Assign A-F
            Select Case DecValue
                Case "10"
                    sTemp = "A"
                Case "11"
                    sTemp = "B"
                Case "12"
                    sTemp = "C"
                Case "13"
                    sTemp = "D"
                Case "14"
                    sTemp = "E"
                Case "15"
                    sTemp = "F"
            End Select
    Else
            'If between 0 and 9 no change
            sTemp = DecValue
    End If

Loop
    DecHexConverter = sTemp
       
End Function