Set font weight of \textbf

Question

I am using Source Sans Pro as my main sans serif font, like so:

\usepackage[semibold]{sourcesanspro}

Using the semibold option works as intended, but it affects all other fonts as well. When I later use another font that does not have semibold characters (case in point: Gentium), supposedly "bold" text is shown plain. If, however, I simply use

\usepackage{sourcesanspro}

everything works fine. How can I restore \textbf{} to use real bold again for all fonts other than Source Sans?

MWE added:

\documentclass[fontsize=12pt,paper=a4,headings=big]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english,ngerman]{babel}

\usepackage{lipsum}
\usepackage{fixltx2e,microtype,leading} 

\usepackage[oldstyle,semibold]{sourcesanspro}
\usepackage{gentium}

\raggedbottom
\leading{14pt}

\begin{document}

\section{Look at my semi-bold title!}
\lipsum[1]

Oh, no, \textbf{this} should be bold!

\end{document}

Yes, I do get a warning:

LaTeX Font Warning: Font shape `T1/gentium/sb/n' undefined(Font)
using `T1/gentium/m/n' instead on input line 21.

I'd rather LaTeX used the bold variant in this case.

Answer 1

The latest version [2013/09/23] of sourcesanspro.sty loads the mweights.sty to exactly cope with such issues. mweights.sty provides means for specifying e.g. different bold weights for roman, typewriter and sans serif fonts. Compiling your code with this newer package gives:

Note that the log contains the information

LaTeX Font Info:    Font shape `T1/gentium/bx/n' in size <12> not available
(Font)              Font shape `T1/gentium/b/n' tried instead on input line 22.

Showing that an attempt has been made to load it at weight bx, but this was not found and b was used instead.