How to set label font to semi bold from code

Hello,
I use this in Xaml to set the font of the label to semi bold.
<Label Text="{Binding Title}" Font="SemiBold,Large" />

I want to make the same, but with C#.

I used this
myLabel.Font = Font.SystemFontOfSize(20, FontAttributes.Bold);

I can't find SemiBold!

Regards,
Mostafa