Samsung Electronics and Microsoft Corporation have been developing open source implementation of .NET platform called .NET Core since 2016. This platform is usually used for implementation of server-side and desktop applications, and Samsung has also adopted .NET Core virtual machine and libraries for Tizen OS. This solution was integrated into various ARM CPU based devices e.g. smart watches, TVs and other electronic devices. Tizen has always supported variety of languages and SDKs for developers. .NET has greatly expanded this variety by supporting new tools and new languages. This paper describes major challenges that we have encountered during integration of .NET to Tizen OS as well as optimizations, which were applied to .NET Core to make applications startup and memory consumption better on variety of devices.