This paper presents a hierarchical architecture model as a systematic approach to building large and complex software intensive systems. This model organizes a software intensive system into a tree-like hierarchical structure. Each entity can be a component, a system or the environment depending on where it is observed. The behavior of each entity is modeled by a behavior tree. One entity can communicate only to its parent entity or direct child entities. To successfully integrate an entity with its parent entity, its behavior and the behavior of its parent must comply with the mutual boundary property.