1. Scalability and Flexibility: Django REST framework is a powerful and flexible framework that allows developers to build scalable and customizable APIs. It provides a wide range of tools and features such as authentication, serialization, and request parsing, which makes it easier to develop complex APIs. On the other hand, Semantic UI is a user interface component framework that focuses on providing pre-built, responsive, and mobile-friendly components for web design. It offers a collection of ready-to-use UI components such as buttons, forms, and grids, allowing developers to quickly build aesthetically pleasing interfaces.

2. Backend vs Frontend: Django REST framework mainly focuses on the backend development of APIs and provides tools for building RESTful APIs using Django. It offers features such as API views, serializers, and authentication, making it an ideal choice for building robust backend systems. On the other hand, Semantic UI is primarily a frontend framework that focuses on providing a set of reusable UI components and styles. It helps in improving the user experience by offering a consistent and visually appealing design for the frontend of the website or application.

3. API Development vs UI Design: Django REST framework is specifically designed for building APIs. It provides features such as content negotiation, pagination, and versioning, making it easy to create RESTful APIs. Developers can use Django's ORM system to define models and create API endpoints for data retrieval and manipulation. Semantic UI, on the other hand, is designed for UI design and provides a range of CSS, Javascript, and HTML components. It offers a set of pre-designed styles and layouts that can be easily customized to match the branding of the website or application.

4. Supported Technologies: Django REST framework is built on top of Django, a high-level Python web framework. As a result, developers can take advantage of Django's features such as the request-response cycle, database connectivity, and authentication system while building APIs. Semantic UI, on the other hand, is a standalone HTML/CSS framework that can be used with any web technology stack. It does not have any specific dependencies and can be integrated with different frontend frameworks such as React, Angular, or Vue.js.

5. Learning Curve: Django REST framework requires a good understanding of Django and its concepts, as it builds upon the Django framework. Developers need to be familiar with the Django ORM, views, and serializers to effectively use Django REST framework for API development. Semantic UI, on the other hand, has a relatively low learning curve as it provides a set of ready-to-use components and styling classes. Developers can quickly start using the components by referencing the documentation and examples provided by Semantic UI.

6. Community and Ecosystem: Django REST framework has a large and active community of developers, which ensures continuous development, bug fixes, and improvements. It has a vast ecosystem of third-party packages and libraries that extend its functionality. Semantic UI also has a supportive community, but it is relatively smaller compared to Django REST framework. However, it provides a comprehensive set of components and themes that can be easily customized and extended.

In Summary, Django REST framework is a backend framework for building scalable and customizable APIs using Django, while Semantic UI is a frontend framework that provides a set of pre-built UI components and styles for web design. Django REST framework focuses on API development and integrates well with Django, while Semantic UI focuses on UI design and can be used with any web technology stack. The learning curve and community size differ between the two frameworks, with Django REST framework requiring a good understanding of Django concepts and having a larger and more active community.