Let's start straight away. In [this](http://books.google.co.in/books?id=32RJvfgkJgwC&q=GaAs#v=snippet&q=GaAs&f=false) book on page 4 Gallium arsenide's bond structure is shown like this:  
![image 1](http://i.imgur.com/HEKlQwu.png)  
$As$ is shown making $5$ covalent bonds.   
Recently I came across [this](http://books.google.ch/books?id=sDCNjgshAmoC&pg=PA65&lpg=PA65&dq=covalent+bonds+GaAs&source=bl&ots=p2M1Ohklcu&sig=pmYV1LpfsSwL9wwgJFJ_OBEw5bE&hl=fr&sa=X&ei=028oU4z2I9Kv7Aao5IGgCQ&ved=0CEwQ6AEwBA#v=onepage&q=covalent%20bonds%20GaAs&f=false) book. The bond structure of $\ce{GaAs}$ is shown like this:  
![image 2](http://i.imgur.com/uPb2Wgv.png). 

Here $\ce{As}$ is shown to make $4$ covalent bonds. 
For sure one of the above quoted images is wrong. But which?  
> To how many $\ce{Ga}$ atoms one $\ce{As}$ atom is connected?  Actually. Please explain  your answer with established reference(s) and also give experimental proof in your answer that supports your answer.   
  
**Edit:**  From the present answers it appears that $As$ makes four covalent bonds, So  
>- Is the book [Electronic Devices and Circuit Theory
 By Boylestad](http://books.google.co.in/books?id=32RJvfgkJgwC&q=GaAs#v=snippet&q=GaAs&f=false) technically incorrect? Should I send an email the authors of this book.