\xRightarrow (text)

Just taking the definition of \xrightarrow and replacing r by R :

\documentclass{article}
\usepackage{amsmath}


\makeatletter
\newcommand{\xRightarrow}[2][]{\ext@arrow 0359\Rightarrowfill@{#1}{#2}}
\makeatother

\begin{document}

$\xrightarrow{\mathit{hello}}$


$\xRightarrow{\mathit{hello}}$


\end{document}

\documentclass{article}
\usepackage{mathtools}
\begin{document}

$\xrightarrow{\text{hello}}$
$\xRightarrow{\text{hello}}$

\end{document}

You can also use underset and overset:

$\underset{\text{hello}} \longrightarrow$

$\overset{\text{hello}} \longrightarrow$

$\underset{\tiny\text{hello}} \longrightarrow$

$\overset{\tiny\text{hello}} \longrightarrow$