IEEE Software-as-a-Service (SaaS) has received significant attention from software providers and users as a software delivery model. Most of the existing companies are transferring their business into a SaaS model. This intensely competitive environment has imposed many challenges for SaaS developers and vendors. SaaS development is a very complex process and SaaS success depends on its architecture design and development. This paper provides a better understanding of SaaS applications architecture phase during the SaaS development process. It focuses mainly on an empirical investigation of key factors of SaaS Architecture phase identified from the systematic literature review. A quantitative survey was developed and conducted to identify key architecture factors for an improved and successful SaaS application. A developed survey was used to test the proposed hypothesis presented in this study. Empirical investigation's results provide evidence that vendors and developers must consider key architecture factors for SaaS development process to stand in the current competitive environment. These key factors include customization, scalability, MTA (Multi-Tenancy Architecture), security, integration, and fault tolerance and recovery management. The main contribution of this paper is to investigate empirically the influence of identified key factors of the architecture on SaaS applications success.