It’s three years since I bought Scottish Mortgage (LSE: SMT) shares for my SIPP. As I recall, I had mixed feelings at the time.

Under talismanic manager James Anderson, who took the helm in 2000, the previously obscure investment trust had grown to be the biggest and most popular in the UK, worth around £25bn. Maybe too popular, because in 2022 it took an absolute beating.

Scottish Mortgage had become a US tech fund by proxy, and when the sector sold off, its shares crashed by half. With Anderson coincidently resigning that year, the outlook was shaky. But I love a bargain and Scottish Mortgage was suddenly at a discount. Banking on a tech rebound, I dived in. I’m thrilled I did.

Why has this trust done so well?

I bought the stock in May and August 2003 at an average price of 709p per share. Today, they trade at 1,531p. I’m up around 115%. That’s before dividends, although with a trailing yield of 0.3%, the income is relatively earthbound.

The last 12 months has been particularly buoyant, with the Scottish Mortgage share price flying 52%. That’s partly down to the upcoming flotation of SpaceX, Elon Musk’s extraterrestrial adventure. It will be valued at between $1.75bn and $2bn when it floats on 12 June, making it the largest IPO in stock market history.

Scottish Mortgage got in early. It took a stake in the privately owned company in December 2018, and purchased more through subsequent funding rounds over the next three years. The trust’s investors have benefited from the stellar growth of SpaceX, without directly buying the stock. That initial holding has grown roughly 1,900%. SpaceX now accounts for a hefty 19.3% of the trust’s total portfolio.

The second biggest holding, Taiwan Semiconductor Manufacturing Company, is just 6.5% of the total, with Nvidia at 5.6%, Bytedance at 4.8%, and Amazon at 4%. Any investor considering it today must also check out what else it holds. They may simply end up doubling down on a string of stocks they already own.

What else am I buying here?

US tech is enjoying a return to form, boosted by the excitement surrounding SpaceX and other super-sized IPOs, such as OpenAI, Anthropic, Databricks, Stripe, and Anduril. Despite this, there’s no way I’d consider upping my personal stake in Scottish Mortgage today.

I’m heavily exposed to tech through both an S&P 500 tracker, FTSE 100 investment trust Polar Capital Technology, and Nvidia. If sceptics are right about that AI bubble, it will explode messily across my portfolio. Also, I’ve learned to mistrust the excitement around IPOs, as share price declines often follow.

There’s understandable excitement around this one. SpaceX opens up massive new possibilities such as massive arrays of orbiting solar panels transmitting energy back to earth. It could prove a great leap for mankind, but it’s also a leap into the dark.

The hype is likely to go into overdrive in the days ahead. Those who are keen to participate may consider feeding some money into the stock. They should also keep some in reserve, for whatever happens next.

Should you invest £5,000 in Scottish Mortgage Investment Trust Plc right now?

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Harvey Jones owns shares in Scottish Mortgage and Nvidia.