Organizations developing software have realized the importance of processes for improving their productivity and quality of their products. There are different Software Process Improvement (SPI) models and methods available to improve processes of software development. If an organization wants to benefit from these models or methods then there is a need to identify Critical Success Factors (CSFs) and Critical Barriers (CBs) that affect the processes of software development in an organization. In Global Software Development (GSD) software projects are developed in an environment where team members reside in different geographical regions. This type of software development crosses the boundary of a company, a city or even a country. In GSD environment organizations play two types of roles. One role is client role and other is vendor role. Client organization acts as client and outsources software projects to other organizations. On the other hand vendor role works as producers or sellers of GSD environment and develops software for the client organizations. Involvement of these two roles in software development makes GSD environment different and complex. Therefore, models and methods made for GSD organizations should be different from conventional software development. There have been fewer SPI models available for GSD environment One such model is SPIIMM model which is only for client role (organizations acting as clients in GSD environment). Purpose of this research work is to devise an SPI model by identifying CSFs and CBs for vendor roles in GSD environment and to extend software process improvement implementation and management model to assist vendor organizations in GSD environment evaluating and improving their process maturity levels. Flow of this research work consists of a systematic literature review, survey from different Pakistani organizations, development of a model called Ext-SPIIMM for vendors of GSD organizations and assessment of developed model with a case study.