The contents of Beamer slides are vertically centered within slides. This is particularly noticeable if there is very little material in the slide.
Use the options t, c or b with \begin{frame}
to have the contents of the slide aligned with the top, center
or bottom of the slide, respectively.  The default option is c.
The following example illustrate this:
\documentclass{beamer} 
\usetheme{Singapore} 
\begin{document} 
 
\begin{frame}[t]{Top alignment} 
 
This is the content of the slide. 
 
\end{frame} 
\end{document} 
\documentclass{beamer} 
\usetheme{Singapore} 
\begin{document} 
 
\begin{frame}[c]{Center alignment (default)} % [c] is the default 
 
This is the content of the slide. 
 
\end{frame} 
\end{document} 
\documentclass{beamer} 
\usetheme{Singapore} 
\begin{document} 
 
\begin{frame}[b]{Bottom alignment} 
 
This is the content of the slide. 
 
\end{frame} 
\end{document} 
You may set the vertical alignment policy for the entire document
by giving one of the options t or b to the
\documentclass.  For instance:
\documentclass[t]{beamer} 
will cause the contents of all slides to be top-aligned.
You can override this for individual slides by using the
c or b options with \begin{frame}.